It is well known to use the mechanical vibration detector as a means for determining whether, or at what point, a machine is in need of repair. One such device, manufactured by SPM Instrument, Inc. of Wallingford, Conn. is known as a VIBRAMETER VIB-10 and includes a piezoelectric device attachable to a machine, for example at an oil input nozzle, and capable of converting vibration through a metallic conductor to an electrical signal that is read as a digital output on a hand-held device. Another similar device manufactured by SPM Instrument, Inc. is called ELECTRONIC STETHESCOPE ELS-12 and includes a hand-held device having an extending, elongated metal probe capable of being disposed against machinery at any desired point and connected through a piezoelectric device for converting the detected vibration into an electrical signal which is amplified through a pair of speaker earphones so that the vibration is detected as a noise level.
These and other similar devices are well known in the art as a maintenance aid in detecting mechanical faults in machinery. Such maintenance aids have been very useful in determining the location of mechanical faults in a machine, such as in industrial machinery, since the machine can be turned on in its normal operating condition and the vibration detector can be attached to the machinery at various points of suspected mechanical failure until the disposition of the mechanical failure is determined. Until the method and device of the present invention, however, such vibration detectors have been practically useless in determining mechanical faults in an automotive device, particularly where it is necessary to operate the automobile in order to place the suspected mechanical device under normal load in order to cause the vibrational symptoms of the mechanical fault.
One particular mechanical fault called brinnelling is a mechanical fault in a wheel bearing assembly wherein rough lines are worn across the wheel bearing race as a result of impact loading or vibration causing vibration of the wheel bearing assembly which, generally, can only be detected when the wheel bearing assembly is under normal load, that is, while the automobile is operated under normal driving conditions with the full weight of the automobile on the wheels. Similarly, other mechanical faults in automotive wheel bearing assemblies, front or rear, and constant velocity (CV) joints usually can only be detected through vibration when the automobile is operated under normal driving conditions with the full weight of the automobile on the wheels. Thus, while some mechanical faults can be detected in an automotive vehicle device by normal operation of the automotive engine without moving the vehicle, for the most part, such vibration detectors such as those described and manufactured by SPM Instrument, Inc. are essentially inoperative for determining mechanical faults in automotive vehicle devices where vibrational fault symptoms occur only when the automotive vehicle is in motion, such as mechanical faults in wheel bearing assemblies and constant velocity joints.
Prior to the method and device of the present invention, it was almost impossible to determine the location of a mechanical fault in an automotive device during movement of the automobile, even when the mechanical fault caused a clearly audible vibration, since the vibration caused by a mechanical fault in an automotive device travels through any interconnected metal parts of the automobile and, therefore, can be audibly detected from many locations other than its source.
The above inadequacies in vibration detection devices for the purpose of determining a mechanical fault in an automotive device, particularly those automotive devices which have mechanical fault symptoms only during movement of the vehicle under normal load conditions, have been overcome in accordance with the method and device of the present invention.